This invention relates to a meter for measuring the volume of a fluid that flows through a line and, more particularly, to such a meter suitable for measuring the volume of a fluid dispensed through a line from a fluid dispenser.
Fluid meters are in widespread use. For example, gasoline dispensing pumps employed for the retail sale of motor fuel include a fluid meter through which gasoline flows, thereby providing a means for determining the quantity of gasoline dispensed. The meter, in turn, is connected to a register which indicates the quantity dispensed, typically in terms of gallons and price.
A meter commonly utilized for such gasoline dispensers is disclosed in U.S. Pat. No. 2,756,726 to Ainsworth. In that disclosure, a meter comprises a multiple piston-in-cylinder hydraulic motor, wherein admission of liquid to the ends of the pistons causes reciprocation thereof, to effect the rotation of a shaft which is adapted to be connected to the register. A rotary valve, coupled to the shaft, admits liquid to the cylinders or permits flow to the outlet connection, in proper timed relation. As distinguished from such meters as the four cylinder cruciform type, or the two-cylinder full double acting arrangement, the Ainsworth meter incorporates the principle of limiting the member of actual cylinders and maintaining desired capacity by providing what may be termed a "blind" or "hypothetical" piston and cylinder, mechanically and hydraulically cooperating with those which are structurally existent.
Ainsworth accomplishes this by so arranging the various ports and the rotary valve that liquid is admitted sequentially to both the crankcase and the head ends of the cylinders, in such a manner that the volume admitted to, or withdrawn from, the crankcase, is equal to the algebraic sum of the volume withdrawn from, or admitted to, the head ends of the cylinders. Two pistons, actuated through the valve mechanism advantageously one hundred and twenty degrees out of phase, thus perform the work equivalent of three pistons. The utilization of this principle accordingly reduces the actual number of cylinders required for a given capacity, with the advantages of reduction of internal friction and pulsation, smoother operation, and also with attendant reduction in manufacturing costs.
The Ainsworth fluid meter, however, is deficient in several respects. For example, because the cylinders are oriented one hundred and twenty degrees apart, they require special piston guide barrels which, together with the cylinders, are bulky and consume a large quantity of space in the crowded cabinet of a typical gasoline multigrade dispenser. Furthermore, it is difficult to mold or cast and machine a housing for such an arrangement of cylinders and guide barrels. Still further, the cylinders require special porting between the valve and the cylinders which restricts the flow of fluid therethrough and decreases meter efficiency. Moreover, an external shaft must extend through the meter housing to drive the register, thus increasing the susceptibility of the meter to leakage.